The invention relates, generally, to bidirectional optical interfaces and, more particularly, to a device for arranging an array of coarse wavelength division multiplexing (CWDM) optical systems in a single, compact and inexpensive device.
It will be appreciated that bidirectional fiber optic transmission systems are an emerging technology for telecommunication networks, backplanes in computers, transmission and sensor technologies and other similar systems. To provide bi-directional flow, a number of solutions exist. One known technology uses a pair of fibers between the endpoints where each fiber carries traffic in one direction. While the use of dual fibers is technologically simple, in certain applications the cost of installing and maintaining dual fibers is prohibitive. As an alternative to the dual fiber solution, a number of single fiber technologies exist for providing a point to point link. One such technology is coarse wavelength division multiplexing (CWDM) in which different wavelengths of light are used to transport data streams over the same optical fiber in opposite directions.
As will be appreciated, in CWDM technology, light of a first wavelength is generated by a laser at a first end of a fiber optic link and is received by a photodiode at a second end of the link, light of a second wavelength is generated by a laser at the second end of the same link and received by a photodiode at the first end of the link. The problem exists that the different wavelengths of light must be combined and split at the endpoints of the fiber optic link. The CWDM couplers that combine and split the light at the endpoints use technology such as fibers bent to critical radii, ball lenses, wavelength selective gratings and the like. All of these technologies require that the light paths emanating from the lasers and the light paths entering the photodiodes must be on adjacent paths. Because the lasers and photodiodes require different semiconductor processes and materials, they cannot both be integrated on the same substrate; therefore, separate integrated circuit chips are required for the lasers and photodiodes. In systems in which a laser array having multiple light paths and a photodiode array also having multiple light paths are used, it is topologically impossible to use standard array lasers, array photodiodes and existing CWDM couplers because current technology does not permit the creation of optical crossovers allowing the adjacent alternating light paths required by the couplers.
Telecommunication network architectures are being developed for providing optical fiber to the customer premise. Typically, fiber links extend between interface cards in a network element such as an optical network unit, switching system or the like and the customer premise. To be cost effective and to support the traffic requirements of a typical network, each interface card should optimally support a minimum of 12 to 24 channels. The use of two fibers, one handling traffic in the upstream direction and one handling traffic in the downstream directions, is prohibitively expensive in such systems because the fiber link is typically on the order of 10,000 meters in length. CWDM technology offers a viable alternative for providing the high density line cards; however a cost effective and compact system for splitting and combining the different wavelengths of light where laser arrays and photodiode arrays are used on the limited space of a line card (a line card being approximately 12.times.8 inches) has not been developed.
In an effort to provide arrays of CWDM data streams, two approaches are known. The first approach uses a single CWDM device that includes the lasers, photodiodes and an CWDM optical splitter system on a single device. This device is relatively robust and has a reasonable level of integration but is relatively large (i.e. 3.times.4 inches) and relies on an expensive optical splitter system. Thus, arranging 24 such integrated systems on the limited area of a line card presents physical design problems. The second approach uses a packaged array of twelve photodiodes, a separate packaged array of twelve lasers, and a separate packaged array of twelve CWDM optical splitter systems. This system reduces the component count over the integrated device design but requires fiber ribbons between the laser, diodes and splitters that are difficult to manage and also present physical design problems.
Thus, an array of CWDM optical systems on a single, compact and inexpensive device that has particular use on a line card in a fiber-based telecommunications network is desired.